Hydrogen-permeable structure and method for manufacture thereof or repair thereof

ABSTRACT

The invention provides a hydrogen permeable structure, which can effectively prevent peeling-off of a hydrogen permeable film and hence has higher durability, and a method of manufacturing the structure. 
     The hydrogen permeable structure has a hydrogen permeable film formed on the surface of or inside a porous support, having a thickness of not more than 2 μm, and containing palladium (Pd). The hydrogen permeable film is formed on the surface of or inside the porous support by supplying a Pd-containing solution and a reducing feed material from opposite sides of the porous support.

TECHNICAL FIELD

The present invention generally relates to a hydrogen permeablestructure and a method of manufacturing the structure, and moreparticularly to a hydrogen permeable structure in which a hydrogenpermeable film is formed in a porous substrate, a method ofmanufacturing the structure, and a method of repairing the structure.

BACKGROUND ART

A hydrogen gas is used as, e.g., fuel for fuel cells and is industriallymanufactured by, e.g., a gaseous fuel denaturing process. With thegaseous fuel denaturing process, for example, a hydrogen gas ismanufactured by denaturing water vapor. A denatured gas contains, inaddition to hydrogen as a primary component, carbon monoxide and carbondioxide as secondary components. Direct use of such a denatured gas as,e.g., fuel for fuel cells deteriorates cell performance. It is thereforerequired to remove the secondary components other than the hydrogen gas,and to refine the denatured gas for obtaining a high-purity hydrogengas. One of known refining methods utilizes a characteristic in which ahydrogen permeable film selectively allows only hydrogen to pass throughthe film. The hydrogen permeable film is formed on a porous support orsubstrate when used.

For example, Japanese Unexamined Patent Application Publication No.11-267477 proposes a hydrogen permeable structure in which a hydrogenpermeable film, such as a Pd film or a Nb film, having a thickness ofabout 0.1 to 20 μm is formed by an ion plating process on the surface ofa porous support made of stainless steel or ceramic, e.g., alumina orsilicon nitride.

Also, Japanese Unexamined Patent Application Publication No. 11-286785proposes a hydrogen permeable structure in which a Pd metal and a metalcapable of alloying with Pd are alternately multi-layered on the surfaceof a porous support by an electroless plating process or an ion platingprocess, and the multi-layers are subjected to heat treatment to form aPd alloy film as a hydrogen permeable film.

Further, Japanese Unexamined Patent Application Publication No. 4-349926proposes a hydrogen gas separation film in which pores of an inorganicporous body with pore sizes of 10 to 10000 Å support therein silica gelhaving an average pore size of 10 to 30 Å, alumina gel having an averagepore size of 15 to 30 Å, or silica-alumina gel having an average poresize of 10 to 20 Å, and a thin film containing palladium is formed as ahydrogen permeable film on the surface of the porous body.

Each of the above-mentioned publications discloses the structure inwhich the hydrogen permeable film is formed on the surface of the poroussupport. However, when those hydrogen permeable structures were used inan atmosphere under various conditions, problems occurred in which thehydrogen permeable film peeled off and durability was poor.

As one example of techniques for depositing Pd on a non-metallicmaterial such as a ceramic, electroless plating using sodium phosphite(NaH₂PO₃) as a reductant is disclosed in “Hyomen Gijutsu (SurfaceTechnology)”, 42, 1146(1991). With this disclosed technique, however, itwas impossible to freely control the plating position. Further, U.S.Pat. No. 5,789,027 discloses a method of depositing a Pd on a substrate,that is, a method in which a Pd compound is dissolved together with ahydrogen gas in a supercritical fluid of CO₂ so as to be supplied ontothe substrate, thereby depositing Pd on the substrate. However, thisdisclosed method requires a fluid in the supercritical state and is noteconomical.

DISCLOSURE OF INVENTION

An object of the present invention is to provide a hydrogen permeablestructure which can effectively prevent peeling-off of a hydrogenpermeable film and hence has higher durability, and to a method ofmanufacturing the structure. According to the method of the presentinvention, the position where a thin film containing Pd is to be formedcan be controlled as desired, no special technique such as asupercritical fluid is required, and defects such as pinholes can easilybe repaired.

The present invention has been accomplished based on the finding that,by forming thin films within pores of a porous support in shapescorresponding to individual pore shapes, a hydrogen permeable structurebeing highly resistant to peeling-off of the thin films and havingsuperior durability can be obtained because peripheries of the thinfilms are supported by a skeleton of the support.

According to the present invention, by supplying a solution containingPd through one surface of a porous support and supplying a solutioncontaining a reductant through the other surface of the porous support,the solution containing Pd and the solution containing the reductantcontact with each other on the surface of or inside the porous support,whereby the Pd is reduced and metallic Pd is deposited. Therefore, thinfilms containing Pd can be formed on the surface of the porous supportand within pores in the surface of the porous support or within poresinside the porous support.

Alternatively, by supplying a reducing gas instead of the solutioncontaining the reductant, metallic Pd is also precipitated by means ofreduction of Pd as described above such that thin films containing Pdcan be formed on the surface of the porous support or within poresinside the porous support. Deposition of metallic Pd continues as longas the solution containing Pd contacts the solution containing thereductant or the reducing gas. In other words, reduction reactioncontinues until the pores of the porous support are sealed off by Pd.

In the case using the reducing gas, by filling a material permeable tothe reducing gas within the pores of the porous support, a thin filmcontaining Pd can be formed on an end surface of the reducing-gaspermeable material. Therefore, the Pd thin film can be formed at adesired position within the porous support.

The solution containing Pd is not limited to a particular one providedthat the solution contains palladium. Examples of such solution includea solution of a Pd complex ion in which ligands, such as NO₂ and NH₃,are coordinated in number not less than two and not more than six, and asolution of palladium chloride or palladium nitrate. Also, the solutioncontaining Pd is preferably a solution containing chlorine andpalladium. Further, the solution containing Pd is preferably a solutioncontaining platinum as well as chlorine and palladium. A hydrogenpermeable film containing Pd to which Pt is added has less solubility tohydrogen at a predetermined temperature than that containing Pd alone.Therefore, an amount of expansion of the crystal lattice of a palladiummetal, i.e., an amount of expansion of the film, can be suppressed. Itis hence possible to reduce compressive stresses caused in the film uponexpansion thereof, and hence to reduce stresses imposed on the interfacebetween the film and a substrate. As a result, physical deterioration ofthe hydrogen permeable film, such as peeling-off and cracks, can begreatly reduced.

The solution containing the reductant is, for example, a solutioncontaining, as a reductant, a phosphate or a hypophosphite, e.g., H₂PO₂⁻ or HPO₃ ²⁻, hydrazine, formaldehyde, dimethylamine borane, or any oftetrahydra borates such as NaBH₄, LiBH₄ and KBH₄. Preferably, thesolution containing the reductant is an alcoholic or aqueous solution inwhich at least one of those reductants is dissolved.

By spraying with a sprayer either or both of the solution containing Pdand the solution containing the reductant in a state of mist, forexample, disturbance at the interface between the Pd-containing solutionand the reductant-containing solution is reduced and the pores can besealed off with thinner films. Accordingly, the spraying method is ableto reduce the amount of deposited Pd to a value not more than 5 g/m² andis more economical. Herein, the term “amount of deposited Pd” representsa value normalized with respect to a Pd deposited area regardless ofshape of the hydrogen permeable structure. More specifically, an area of1 to 10 cm² of the hydrogen permeable structure, in which Pd has beendeposited, is cut out from any desired position, and a cut-out specimenis dissolved in an acid. The Pd concentration of the thus obtainedsolution is analyzed with plasma emission spectroscopic analysis tocalculate a total amount of Pd. Then, the amount of deposited Pd isobtained by dividing the total amount of Pd by the area of the specimen.

The reducing gas is preferably a hydrogen gas, but any other suitablegas may be mixed in a hydrogen gas for control of the reaction velocity.Further, the gas permeable material is preferably paraffin. Paraffin ispermeable to hydrogen and can be dissolved and removed with an organicsolvent, such as dichloromethane.

Preferably, thin films formed inside the porous support and containingPd have an average thickness of not more than 2 μm and not less than0.01 μm. Also, thin films formed on the surface of the porous supportand containing Pd have an average thickness of not more than 2 μm andnot less than 0.01 μm. In the thin films formed inside or on the surfaceof the porous support and containing Pd, the deposition rate of Pd ispreferably not more than 5 g/m². The porous support is preferably aporous body of silicon nitride or a metallic porous body.

Further, the porous support has holes in the surface thereof, andpreferably is provided with a porous oxide layer, or a layer of metal ormetal oxide having an average particle size of not more than 2 μm suchthat the holes are covered therewith. With such structure, since theholes in the surface of the porous support are filled, making thesurface even, the hydrogen permeable film can be formed in a dense statefree from pinholes when it is formed on the surface of the poroussupport. Accordingly, the permeability characteristics of the hydrogenpermeable film can be improved. In such a case, preferably, the oxidelayer contains at least one selected from the group consisting ofaluminum oxide (Al₂O₃), silicon dioxide (SiO₂) and zirconium oxide(ZrO₂). The oxide layer is more preferably made of aluminum oxide.

In the hydrogen permeable structure in which a Pd-containing thin filmhas been formed on the surface of or inside the porous support thereof,defects of the Pd-containing thin film, such as pinholes, can easily berepaired by supplying the solution containing Pd onto one surface of thehydrogen permeable structure and supplying the solution containing thereductant onto the other surface of the hydrogen permeable structure,since thereby a metal containing Pd can be deposited in the pinholeswith priority. In that case, a similar effect is also obtained by usinga reducing gas instead of the solution containing the reductant.

If a hydrogen permeable structure includes a layer in which pores aresealed off by depositing a metal containing Pd in a porous supportand/or porous powder, its durability can be further improved. In such ahydrogen permeable structure, an amount of nitrogen permeable throughthe structure can be reduced to a level not more than 0.6 ml/min/cm²under a differential pressure of 1 atmospheric pressure. As a result,hydrogen having a higher purity can be obtained.

Additionally, a Pd-containing film can be made denser by performing heattreatment of the Pd-containing film in a non-oxidizing atmosphere, e.g.,a vacuum, a nitrogen atmosphere or a hydrogen atmosphere, after thePd-containing film has been formed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows one embodiment of the present invention in which a reducingfeed material is a solution.

FIG. 2 shows one embodiment of the present invention in which a reducingfeed material is a gas.

FIG. 3 shows a cross-section of one example of a hydrogen permeablestructure according to the present invention. The pores of a poroussupport are omitted in the drawing.

FIG. 4 is a schematic sectional view of one embodiment of the presentinvention, showing a state in which hydrogen permeable films are formedon the surface of and inside the porous support with alumina powderfilled on the surface thereof.

FIG. 5 is a schematic sectional view of one embodiment of the presentinvention, showing a state in which hydrogen permeable films are formedonly inside the porous support with alumina powder filled on the surfacethereof.

BEST MODE FOR CARRYING OUT THE INVENTION

A hydrogen-gas separating structure as one embodiment of a hydrogenpermeable structure of the present invention is constructed by formingmetallic thin films, containing Pd, within pores of a porous support orthe surface of the porous support.

The porous support has no special limitation on materials thereof, andcan be made of a metallic material such as SUS316L, or any of ceramicsincluding various oxides, e.g., aluminum oxide, and various nitrides,e.g., silicon nitride. Among ceramics, a porous body of silicon nitrideis particularly preferable. The pore size of the porous support is notlimited to a particular value, but it is preferably not more than 1 μmand not less than 0.1 μm. If a porous support having the pore size over1 μm is used, the thin films formed in pores and containing Pd would betoo thick, thus resulting in being less economical and deterioration ofhydrogen permeability. If the pore size is less than 0.1 μm, the thinfilms would be too thin, thus resulting in problems in terms ofdurability.

According to the manufacturing method of the present invention, asolution feed material containing Pd is supplied through one surface ofthe porous support, and a reducing feed material is supplied through theother surface thereof. Upon contact of the solution containing Pd andthe reducing feed material, Pd is reduced and metallic Pd is deposited,whereby the thin film(s) containing Pd can be formed on the surface ofthe porous support or within the pores inside the porous support. Also,by adjusting the concentration and reaction conditions of either or bothof the Pd containing solution and the reducing feed material, the thinfilms containing Pd can be formed only inside the porous support, i.e.,in a region inward of the surface of the porous support. Since the thusobtained thin films are formed within the pores of the porous support,those thin films are surrounded by the skeleton (matrix) of the poroussupport and high durability can be obtained. Particularly, when the thinfilms are formed only inside the porous support, those thin films areentirely surrounded by the skeleton (matrix) of the porous support andhence higher durability can be obtained. Note that, if both the feedmaterials are supplied onto the same surface, the thin films containingPd cannot be formed in the porous support because fine particles ofmetallic Pd start deposition immediately after the feed materials are incontact with each other.

The hydrogen permeability of the hydrogen permeable film is in reverseproportion to a film thickness. For example, the permeability ofhydrogen through a 2 μm-thick film is 10 times the permeability througha 20 μm-thick film. With a 10-time increase in hydrogen permeabilitythrough the film, the film surface area required for obtaining the sameamount of hydrogen permeable through the film is reduced to {fraction(1/10)}. Thus, when the thickness of the hydrogen permeable film isreduced to {fraction (1/10)}, the required weight of the film is reducedto {fraction (1/100)}. According to the present invention, therefore,since a dense hydrogen permeable film having good hydrogen permeabilitycan be formed in thickness of not more than 2 μm, it is possible toprovide a low-cost, high-performance and compact hydrogen permeablestructure. Conversely, if the film thickness is less than 0.01μ,problems such as the deterioration of the hydrogen separationperformance and a decrease of durability would occur.

In the solution containing Pd, any of a palladium complex, palladiumchloride, palladium acetate, etc. is usable as a solute. Also, byadjusting a PH of the solution with acids or bases, such as hydrochloricacid and acetic acid, the maximum solubility of the solute can beadjusted and hence the reduction reaction velocity can also be adjusted.Further, by employing a solution in which a platinum compound, a silvercompound, or the like is dissolved together with a Pd compound, thinfilms of a Pd—Pt alloy or a Pd—Ag alloy can be formed. A preferableexample of the platinum compound is platinum chloride or a platinumorganic complex, and a preferable example of the silver compound issilver chloride or a silver organic complex.

The reducing feed material may be in the form of a liquid or gas. In thecase of a liquid, a solution containing a reductant is usable. Whendimethylamine borane, NaBH₄, LiBH₄, KBH₄, or the like is used as thereductant, not only water but also alcohol can be used as a solvent.However, in the case of LiBH₄ in particular, an alcoholic solution ispreferably used since LiBH₄ decomposes upon reaction with water, thoughit has maximum reducing power. Using an alcoholic solution isadvantageous in that, by increasing the size of a hydrophobic radical inalcohol, affinity with an aqueous solution containing Pd ions can bereduced, and hence a more local and thinner Pd-containing film can beformed. Further, in the case where both of the Pd-containing solutionand the reductant-containing solution are used, by spraying either orboth of the solutions in a state of mist with a sprayer, for example,disturbance at the interface between the Pd-containing solution and thereductant-containing solution is reduced, and hence the pores can besealed off with thinner films. Accordingly, the spraying method is ableto reduce the amount of Pd used and is more economical.

In the case using gas, any reducing gas can be used, but a preferableexample is hydrogen. Also, a gas mixture with another kind of gas mayalso be used to control the reaction velocity. Further, by filling theporous support beforehand with a material that is gas permeable and canbe removed later, it is possible to control the position where thehydrogen permeable film is to be formed. One example of such a fillingmaterial is paraffin. Paraffin is hydrogen permeable. For example, ifparaffin is filled to half the thickness of the porous support and thePd-containing solution is supplied from the side that is not filled withparaffin and hydrogen is supplied from the side that is filled withparaffin, then, the supplied hydrogen passes through the paraffin andreaches the paraffin surface, whereupon reduction reaction occursbetween the Pd-containing solution and hydrogen gas, and ahydrogen-permeable film containing Pd can be formed on the paraffinsurface. By adjusting the amount of paraffin filled, the position wherethe film is to be formed can be controlled. After the hydrogen-permeablefilm containing Pd has been formed, the paraffin can be dissolved andremoved using an organic solvent, e.g., dichloromethane.

When the solution containing Pd ions contacts the reducing feedmaterial, Pd is reduced and a metal containing Pd is deposited. Themetal is gradually deposited within the pores of the porous support suchthat eventually the metal fills the pores at a certain thickness andseals off the pores. The reduction reaction continues until the poresare completely sealed off. The thickness of the thin films containing Pdand the position where the thin films are formed inside the poroussupport can be controlled in accordance with, e.g., the pore size of theporous support, the concentration of the Pd-containing solution, theconcentration of the reductant in the reducing feed material, and thereaction temperature, as well as the kind of solvent and a PH when thereducing feed material is a solution.

The porous support has no limitation in its shape. In the case of a flatplate, the Pd-containing solution and the reductant-containing solutionmay be supplied to the plate from opposite sides. In the case of ahollow cylinder, those solutions can be supplied through an innerperipheral surface and an outer peripheral surface of the cylinder.

In the method of manufacturing the hydrogen permeable structureaccording to the present invention, the reduction reaction continuesuntil the pores are completely sealed off, as described above. Thismeans that when defects such as pinholes are present in the formedhydrogen permeable film, the reduction reaction occurs first in thosedefects such as pinholes. In other words, defects such as pinholescaused in the hydrogen permeable structure can easily be repaired byapplying the method according to the present invention since a metalcontaining Pd can be thereby deposited only in the defects such aspinholes. The method of the present invention is also, applicable to thecase of regenerating a failed structure.

Further, a feature of the hydrogen permeable structure according to thepresent invention is that it has a layer formed by depositing a metalcontaining Pd in the porous support or porous powder so as to sealed offpores, and that the amount of nitrogen permeable through the structureis small: not more than 0.6 ml/min/cm² under a differential pressure of1 atmospheric pressure. Accordingly, hydrogen having a high purity canbe obtained.

EXAMPLE 1

A disk having a diameter of 22 mm and a thickness of 1 mm was preparedby machining a porous sintered body of silicon nitride 1 with a poresize of 0.3 μm. The disk was glass-bonded, as shown in FIG. 1, to oneend surface of a cylindrical holder 2 made of a dense ceramic and havingan outer diameter of 22 mm. After pouring, in the dense ceramiccylindrical holder, 20 ml of a solution that was prepared by dissolving30 g of Pd(NO₃)₂ in 1 liter of 1N-nitric acid, the cylinder was immersedin a 1.0 g/l aqueous solution of dimethylamine borane 4 for 2 minuteswithin a thermostatic chamber 5. The solution temperature was adjustedso as to be maintained at 25° C. using a heater and a cooler (notshown). After 2 minutes, the grass-bonded disk and cylindrical holderwere removed from the thermostatic chamber, and a porous support diskwas obtained by disconnecting the glass bonding. The surface of theporous support disk, which had been subjected to the aqueous solution ofdimethylamine borane, had a black discoloration and exhibited electricalcontinuity. It was hence confirmed that a Pd metal was deposited.

The thus obtained disk was heat-treated at a temperature of 500° C. for1 hour in hydrogen under 101.325 kPa (1 atmospheric pressure). After theheat treatment, the Pd structure was measured by X-ray diffraction andconfirmed to be of face-centered cubic lattice. Then, the disk was cutand the cut section was observed with an electron microscope. As aresult, it was confirmed that Pd was deposited in pores up to a depth of0.5 μm from the surface having a black discoloration, and Pd thin filmsof 0.5 μm thickness were formed in the pores.

The hydrogen permeability of the hydrogen permeable structure obtainedas described above was measured. More specifically, the permeationamount of hydrogen or nitrogen was measured by introducing a pure gas ofhydrogen or nitrogen at a temperature of 400° C. through one surface ofthe hydrogen permeable structure under a pressure difference of 101.325kPa (1 atmospheric pressure). As a result, it was confirmed that thepermeation amount of hydrogen was 80 ml/min/cm² and the permeationamount of nitrogen was 0.05 ml/min/cm², and hence that practically onlyhydrogen was allowed to selectively pass through the structure. Also, aheat cycle test of 500 cycles was conducted between temperature of 400°C. and room temperature in a hydrogen gas atmosphere of 101.325 kPa (1atmospheric pressure). After the test, peeling-off and cracks of thefilms were inspected by visual observation and by using an electronmicroscope, respectively. As a result, no physical deterioration of thefilms, such as peeling-off and cracks, was observed.

EXAMPLE 2

A porous disk made of silicon nitride and a cylindrical holder made of adense ceramic, similar to those used in EXAMPLE 1, were prepared. Afterpouring 20 ml of a solution that was prepared by dissolving 30 g ofPd(NO₂)₂(NH₃)₂ in 1 liter of 1N-nitric acid, into the dense ceramiccylindrical holder, the cylinder was immersed in a solution, which wasprepared by dissolving 2.0 g of NaH₂PO₂ in 1 liter of pure water, for 2minutes within a thermostat. The solution temperature was adjusted so asto be maintained at 25° C. using a heater and a cooler (not shown).After 2 minutes, the grass-bonded disk and cylindrical holder wereremoved from the thermostatic chamber, and a porous support disk wasobtained by disconnecting the glass bonding.

The thus obtained disk was measured for the hydrogen permeability in thesame manner as in EXAMPLE 1. As a result, it was confirmed that thepermeation amount of hydrogen was 60 ml/min/cm² and the permeationamount of nitrogen was 0.03 ml/min/cm², and hence that practically onlyhydrogen was allowed to selectively pass through the disk.

EXAMPLE 3

A porous disk made of silicon nitride and a cylindrical holder made of adense ceramic, similar to those used in EXAMPLE 1, were prepared. Afterpouring 20 ml of a solution that was prepared by dissolving 30 g ofPd(NO₂)₂(NH₃)₂ in 1 liter of 1N-nitric acid, into the dense ceramiccylindrical holder, the cylinder was immersed in a solution, which wasprepared by dissolving 3.0 g of hydrazine in 1 liter of pure water, for2 minutes within a thermostat. The solution temperature was adjusted soas to be maintained at 25° C. using a heater and a cooler (not shown).After 2 minutes, the grass-bonded disk and cylindrical holder wereremoved from the thermostatic chamber, and a porous support disk wasobtained by disconnecting the glass bonding.

The thus obtained disk was measured for the hydrogen permeability in thesame manner as in EXAMPLE 1. As a result, it was confirmed that thepermeation amount of hydrogen was 60 ml/min/cm² and the permeationamount of nitrogen was 0.03 ml/min/cm², and hence that practically onlyhydrogen was allowed to selectively pass through the disk.

EXAMPLE 4

A porous disk made of silicon nitride 1 and a cylindrical holder made ofa dense ceramic 2, similar to those used in EXAMPLE 1, were prepared.After glass-bonding the disk to one end surface of the dense ceramiccylindrical holder as in EXAMPLE 1, a solution of Pd(NO₃)₂ 3 was pouredinto the cylindrical holder and, as shown in FIG. 2, the cylindricalholder was placed in a thermostatic chamber 5 such that the surface ofthe Pd(NO₃)₂ was positioned outside the thermostat. Then, a hydrogen gasof 101.325 kPa (1 atmospheric pressure) was introduced into thethermostat. After introducing the hydrogen gas for 5 minutes, the porousdisk made of silicon nitride was removed from the thermostatic chamber.The surface of the disk, which had been subjected to the hydrogen gas,had a black discoloration and exhibited electrical continuity. It washence confirmed that a Pd metal was deposited. The thus obtained diskwas cut and the cut section was observed with an electron microscope. Asa result, it was confirmed that Pd was deposited in pores up to a depthof 0.8 μm from the surface having a black discoloration, and Pd thinfilms of 0.8 μm thickness were formed in the pores. Note that thin filmscontaining Pd can also be formed by putting into the thermostaticchamber, as in FIG. 1, the entirety of the container made of the poroussilicon nitride disk and the dense ceramic cylindrical holder, in whichthe Pd(NO₃)₂ solution is filled. This method, however, is uneconomicalbecause the reduction reaction occurs at the surface of thePd-containing solution in the container as well and Pd is also depositedthere.

The hydrogen permeability of the hydrogen permeable structure obtainedas described above was measured in the same manner as in EXAMPLE 1. As aresult, it was confirmed that the permeation amount of hydrogen was 60ml/min/cm² and the permeation amount of nitrogen was 0.03 ml/min/cm²,and hence that practically only hydrogen was allowed to selectively passthrough the structure. Also, a heat cycle test of 500 cycles wasconducted between temperature of 400° C. and room temperature in ahydrogen gas atmosphere of 101.325 kPa (1 atmospheric pressure). Afterthe test, peeling-off and cracks of thin films were inspected by visualobservation and by using an electron microscope, respectively. As aresult, no physical deterioration of the films, such as peeling-off andcracks, was observed.

EXAMPLE 5

A disk having a diameter of 22 mm and a thickness of 1 mm was preparedby machining a porous sintered body of silicon nitride having a poresize of 0.3 μm. Paraffin having the melting point of 70° C. was filledin the disk up to a depth of 0.5 mm. The disk was glass-bonded to oneend surface of a cylindrical holder made of a dense ceramic and havingan outer diameter of 22 mm such that the disk surface filled with theparaffin was faced outward. After pouring 20 ml of a solution that wasprepared by dissolving 30 g of Pd(NO₃)₂ in 1 liter of 1N-nitric acid,into the dense ceramic cylindrical holder, the cylindrical holder wasput into a thermostat. A hydrogen gas of 101.325 kPa (1 atmosphericpressure) was then, introduced into the thermostat and such a conditionwas held for 5 minutes, during which period the temperature in thethermostat was maintained at 25° C. After 5 minutes, the porous diskmade of silicon nitride was removed from the thermostat. No change wasobserved in the external appearance of the disk. The disk was cut andthe cut section was observed with an electron microscope. As a result,as schematically illustrated in FIG. 3, it was confirmed that a Pd film8 was deposited in pores with a thickness of 0.3 μm from the forefrontsurface of the filled paraffin 9, and Pd thin films were formed in thepores, in thickness of 0.3 μm from the position of 0.5 mm in thedirection of thickness of the porous disk made of silicon nitride.

The paraffin was dissolved and removed by three repetitions of immersingthe hydrogen permeable structure obtained as described above indichloromethane for 15 minutes, replacing the dichloromethane with newdichloromethane, at each 15-minute immersion. After drying the hydrogenpermeable structure, it was heat-treated at a temperature of 500° C. for1 hour in hydrogen under 101.325 kPa (1 atmospheric pressure). Thehydrogen permeability of the thus obtained hydrogen permeable structurewas measured in the same manner as in EXAMPLE 1. As a result, it wasconfirmed that the permeation amount of hydrogen was 90 ml/min/cm² andthe permeation amount of nitrogen was 0.05 ml/min/cm², and hence thatpractically only hydrogen was allowed to selectively pass through thestructure. Also, a heat cycle test of 500 cycles was conducted betweentemperature of 400° C. and room temperature in a hydrogen gas atmosphereof 101.325 kPa (1 atmospheric pressure). After the test, peeling-off andcracks of the films were inspected by visual observation and by using anelectron microscope, respectively. As a result, no physicaldeterioration of the films, such as peeling-off and cracks, wasobserved.

EXAMPLE 6

As in EXAMPLE 1, an assembly of a porous disk made of silicon nitrideand a cylindrical holder made of a dense ceramic was prepared byglass-bonding them. A solution prepared by dissolving 27 g of Pd(NO₃)₂and 3 g of Pt(NO₂)₂(NH₃)₂ in 1 liter of 1N-nitric acid was poured intothe dense ceramic cylindrical holder. Then, the cylinder was immersed ina 1.0 g/l aqueous solution of dimethylamine borane for 2 minutes withina thermostat. The solution temperature was adjusted so to be maintainedat 25° C. After 2 minutes, the grass-bonded disk and cylindrical holderwere removed from the thermostatic chamber, and a porous support diskwas obtained by disconnecting the glass bonding. The thus obtained diskwas heat-treated at a temperature of 500° C. for 1 hour in hydrogenunder 101.325 kPa (1 atmospheric pressure). Then, the disk was cut andthe cut section was observed with an electron microscope. As a result,it was confirmed that a metal was deposited in pores up to a depth of0.5 μm, and metallic thin films of 0.5 μm thickness were formed in thepores. The composition of the metallic thin films was examined byfluorescent X-ray analysis, and it was found to be 89 wt % Pd and 11 wt% Pt.

The hydrogen permeability of the hydrogen permeable structure obtainedas described above was measured in the same manner as in EXAMPLE 1. As aresult, it was confirmed that the permeation amount of hydrogen was 90ml/min/cm² and the permeation amount of nitrogen was 0.05 ml/min/cm²,and hence that practically only hydrogen was allowed to selectively passthrough the structure. Also, a heat cycle test of 500 cycles wasconducted between the temperature of 400° C. and room temperature in ahydrogen gas atmosphere of 101.325 kPa (1 atmospheric pressure). Afterthe test, peeling-off and cracks of the films were inspected by visualobservation and by using an electron microscope, respectively. As aresult, no physical deterioration of the films, such as peeling-off andcracks, was observed.

EXAMPLE 7

A disk having a diameter of 22 mm and a thickness of 1 mm was preparedusing porous SUS316L with a filtration size of 0.5 μm. The disk wassilver-brazed to one end surface of a cylinder made of a dense SUS316Land having an outer diameter of 22 mm. After pouring the same solutionas used in EXAMPLE 1 into the cylinder, the cylinder was immersed in asolution of a reductant (propanol) within a thermostat, the solutionbeing the same as used in EXAMPLE 1. After 10 minutes, the porous diskmade of porous SUS316L was removed from the thermostatic chamber.

The thus obtained disk was heat-treated at a temperature of 500° C. for1 hour in hydrogen under 101.325 kPa (1 atmospheric pressure). After theheat treatment, the disk was cut and the cut section was observed withan electron microscope. As a result, it was confirmed that Pd wasdeposited in pores up to a depth of 1.5 μm, and Pd thin films of 1.5 μmthickness were formed in the pores.

The hydrogen permeability of the hydrogen permeable structure obtainedas described above was measured in the same manner as in EXAMPLE 1. As aresult, it was confirmed that the permeation amount of hydrogen was 30ml/min/cm² and the permeation amount of nitrogen was 0.01 ml/min/cm²,and hence that practically only hydrogen was allowed to selectively passthrough the structure. Also, a heat cycle test of 500 cycles wasconducted between the temperature of 400° C. and room temperature in ahydrogen gas atmosphere of 101.325 kPa (1 atmospheric pressure). Afterthe test, peeling-off and cracks of the films were inspected by visualobservation and by using an electron microscope, respectively. As aresult, no physical deterioration of the films, such as peeling-off andcracks, was observed.

EXAMPLE 8

A disk having a diameter of 22 mm and a thickness of 1 mm was preparedby machining a porous sintered body of silicon nitride having a poresize of 0.3 μm. One surface of the disk was polished with a polishingsolution including γ-alumina powder of a 0.05-μm average particle sizedispersed therein. Also, the γ-alumina powder was filled into holes ofthe disk surface to make it flat. Subsequently, the disk filled with theγ-alumina powder was sintered in an atmosphere at 750° C. for 30minutes. The thus sintered disk was glass-bonded, as shown in FIG. 1, toone end surface of a cylindrical holder made of a dense ceramic andhaving an outer diameter of 22 mm, at which time, the disk surfaceflattened with the y-alumina powder was positioned to face outward ofthe cylinder (downward in FIG. 1). After pouring 20 ml of a solutionprepared by dissolving 25 g of PdCl₂ in 1 liter of 1N-hydrochloric acid,into the dense ceramic cylindrical holder, the holder was immersed in a1.0 g/l aqueous solution of dimethylamine borane for 2 minutes within athermostat. The solution temperature was adjusted so as to be maintainedat 25° C. using a heater and a cooler (not shown). After 2 minutes, thegrass-bonded disk and cylindrical holder were removed from thethermostatic chamber, and a porous support disk was obtained bydisconnecting the glass bonding. The surface of the porous support disk,which had been subjected to the aqueous solution of dimethylamineborane, had metallic luster and exhibited electrical continuity. It washence confirmed that a Pd metal was deposited.

The thus obtained disk was heat-treated at a temperature of 500° C. for1 hour in hydrogen under 101.325 kPa (1 atmospheric pressure). After theheat treatment, the disk was cut and the cut section was observed withan electron microscope. FIG. 4 schematically shows the observed section.As a result of the observation, it was confirmed that the γ-alumina 10was filled into pores of the porous silicon nitride up to a depth of 0.5μm from the Pd-deposited disk surface and Pd 8 was deposited in gapsbetween particles of the γ-alumina powder. It was also confirmed that Pd8 deposited on the disk surface was in the form of a thin film having athickness of 0.1 μm. Further, as a result of observing the disk surfacewith a Scanned Electron Microscope (SEM), it was confirmed that nearly100% area of the entire disk surface was covered with Pd.

The hydrogen permeability of the hydrogen permeable structure obtainedas described above was measured in the same manner as in EXAMPLE 1. As aresult, it was confirmed that the permeation amount of hydrogen was 120ml/min/cm² and the permeation amount of nitrogen was 0.05 ml/min/cm²,and hence that practically only hydrogen was allowed to selectively passthrough the structure. Also, a heat cycle test of 500 cycles wasconducted between the temperature of 400° C. and room temperature in ahydrogen gas atmosphere of 101.325 kPa (1 atmospheric pressure). Afterthe test, peeling-off and cracks of the film were inspected by visualobservation and by using an electron microscope, respectively. As aresult, no physical deterioration of the film, such as peeling-off andcracks, was observed.

EXAMPLE 9

A disk having a diameter of 22 mm and a thickness of 1 mm was preparedby machining a porous sintered body of silicon nitride having a poresize of 0.3 μm. One surface of the disk was polished with a polishingsolution including γ-alumina powder of a 0.05-μm average particle sizedispersed therein. Also, the γ-alumina powder was filled into holes inthe disk surface to make it flat. The disk filled with the γ-aluminapowder was glass-bonded to one end surface of a cylindrical holder madeof a dense silicon nitride and having an outer diameter of 22 mm, atwhich time, the disk surface flattened with the γ-alumina powder waspositioned to face outward of the cylinder. Then, 20 ml of a solutionprepared by dissolving 25 g of PdCl₂ in 1 liter of 1N-hydrochloric acidwas poured into the dense silicon-nitride cylindrical holder. A2-propanol solution containing 0.25 g/l of NaBH₄ was filled into asprayer, and mist of the solution was sprayed on the outer surface ofthe bonded disk. With the spray of the solution in the state of mist,drips falling from the disk were black in the initial period, thusshowing the progress of reduction reaction. After continuing to sprayfor about 5 minutes, falling drips became transparent, whereupon it wasdetermined that the reduction reaction was completed. Then, spraying ofthe solution was stopped, and a porous support disk was obtained bydisconnecting the glass bonding. The surface of the porous support disk,which had been subjected to the spray of the solution, was black andexhibited electrical continuity. It was hence confirmed that a Pd metalwas deposited.

The thus obtained disk was heat-treated at a temperature of 500° C. for1 hour in hydrogen under 101.325 kPa (1 atmospheric pressure). After theheat treatment, the disk was cut and the cut section was observed withan electron microscope. FIG. 5 schematically shows the observed section.As a result of the observation, it was confirmed that the γ-alumina 10was filled into pores of the porous silicon nitride up to a depth of 0.5μm from the Pd-deposited disk surface and Pd 8 was deposited in gapsbetween particles of the γ-alumina powder. It was also confirmed that Pdwas not deposited on the surface of the porous disk made ofsilicon-nitride.

The hydrogen permeability of the hydrogen permeable structure obtainedas described above was measured in the same manner as in EXAMPLE 1. As aresult, it was confirmed that the permeation amount of hydrogen was 140ml/min/cm² and the permeation amount of nitrogen was 0.02 ml/min/cm²,and hence that practically only hydrogen was allowed to selectively passthrough the structure. Also, a heat cycle test of 1000 cycles wasconducted between the temperature of 400° C. and room temperature in ahydrogen gas atmosphere of 101.325 kPa (1 atmospheric pressure). Afterthe test, peeling-off and cracks of the film were inspected by visualobservation and by using an electron microscope, respectively. As aresult, no physical deterioration of the film, such as peeling-off andcracks, was observed. Thus, it was found that by forming Pd-containingthin films only inside the porous support the durability was greatlyimproved. Further, Pd deposited in the disk was dissolved in aqua regiaand subjected to Inductively Coupled Plasma (ICP) emission spectroscopicanalysis. As a result, the amount of Pd was 1.5g/m². Accordingly, it wasfound that the amount of Pd was reduced to half by employing thespraying method because the amount of Pd deposited in the hydrogenpermeable structure by the method of immersing the disk in thereductant-containing solution, as with EXAMPLE 8, was 3.0 g/m².

EXAMPLE 10

The surface of the disk-shaped hydrogen permeable structure obtainedwith EXAMPLE 8, on which a Pd film was formed, was artificially abradedand flawed 10 times using a No. 1200 polishing paper. The amount ofnitrogen having passed through the flawed disk was measured in the samemanner as in EXAMPLE 1. As a result, the measured amount was 15ml/min/cm², which was considerably increased from 0.05 ml/min/cm², i.e.,the amount measured prior to flawing of the disk. In other words, it wasevident that the Pd thin film was partly broken.

A Pd film was formed on the flawed disk in the same manner and under thesame conditions as those in EXAMPLE 8. The disk thus repaired wasmeasured for permeability of hydrogen or nitrogen in the same manner asin EXAMPLE 1. As a result, it was confirmed that the permeation amountof hydrogen was 120 ml/min/cm² and the permeation amount of nitrogen was0.05 ml/min/cm². It was hence found that the flaws were repaired and thedisk was restored to its original permeability.

INDUSTRIAL APPLICABILITY

According to the present invention, as described above, physicaldeterioration of the hydrogen permeable film, such as peeling-off andcracks, can be greatly reduced and durability of the hydrogen permeablefilm can be increased. Also, the position where a thin film containingPd is to be formed can be controlled as desired, and defects such aspinholes can easily be repaired.

What is claimed is:
 1. A method of manufacturing a hydrogen permeablestructure, comprising the steps of supplying a solution containing Pdonto one surface of a porous support and supplying a solution containinga reductant onto the other surface of said porous support, therebyforming a thin film containing Pd on the surface of said porous supportor inside said porous support.
 2. A method of manufacturing a hydrogenpermeable structure, comprising the steps of supplying a solutioncontaining Pd onto one surface of a porous support and supplying areducing gas onto the other surface of said porous support, therebyforming a thin film containing Pd on the surface of said porous supportor inside said porous support.
 3. A method of manufacturing a hydrogenpermeable structure according to claim 2, further comprising the stepsof filling a gas permeable material within pores of said porous support,thereby forming a thin film containing Pd on an end surface of said gaspermeable material.
 4. A method of manufacturing a hydrogen permeablestructure according to claim 1, wherein the solution containing Pdcontains a complex ion in which ligands are coordinated in number of notless than two and not more than six per one Pd atom.
 5. A method ofmanufacturing a hydrogen permeable structure according to claim 2,wherein the solution containing Pd contains a complex ion in whichligands are coordinated in number of not less than two and not more thansix per one Pd atom.
 6. A method of manufacturing a hydrogen permeablestructure according to claim 1, wherein the solution containing Pd is asolution containing chlorine and palladium.
 7. A method of manufacturinga hydrogen permeable structure according to claim 2, wherein thesolution containing Pd is a solution containing chlorine and palladium.8. A method of manufacturing a hydrogen permeable structure according toclaim 1, wherein the solution containing Pd is a solution containingchlorine, palladium and platinum.
 9. A method of manufacturing ahydrogen permeable structure according to claim 2, wherein the solutioncontaining Pd is a solution containing chlorine, palladium and platinum.10. A method of manufacturing a hydrogen permeable structure accordingto claim 1, wherein the solution containing the reductant contains atleast one of H₂PO₂ ⁻ and HPO₃ ²⁻.
 11. A method of manufacturing ahydrogen permeable structure according to claim 1, wherein the solutioncontaining the reductant contains dimethylamine borane.
 12. A method ofmanufacturing a hydrogen permeable structure according to claim 1,wherein the solution containing the reductant is a solution in which atleast one of NaBH₄, LiBH₄ and KBH₄ is dissolved.
 13. A method ofmanufacturing a hydrogen permeable structure according to claim 1,wherein one or both of the solution containing Pd and the solutioncontaining the reductant are sprayed in a state of mist.
 14. A method ofmanufacturing a hydrogen permeable structure according to claim 2,wherein the reducing gas is a hydrogen gas.
 15. A method ofmanufacturing a hydrogen permeable structure according to claim 3,wherein the gas permeable material is paraffin.
 16. A method ofrepairing a hydrogen permeable structure, comprising the steps ofsupplying a solution containing Pd onto one surface of said hydrogenpermeable structure in which a thin film containing Pd has been formedon the surface of or inside a porous support and supplying a solutioncontaining a reductant onto the other surface of said hydrogen permeablestructure, thereby forming a thin film containing Pd in pinholes orother defects of said former thin film containing Pd.
 17. A method ofrepairing a hydrogen permeable structure, comprising the steps ofsupplying a solution containing Pd through one surface of said hydrogenpermeable structure in which a thin film containing Pd has been formedon the surface of or inside a porous support and supplying a reducinggas through the other surface of said hydrogen permeable structure,thereby forming a thin film containing Pd in pinholes or other defectsof said former thin film containing Pd.
 18. A hydrogen permeablestructure wherein thin films formed on and/or in a porous support andcontaining Pd have an average thickness of not more than 2 μm.
 19. Ahydrogen permeable structure according to claim 18, wherein thin filmsformed inside said porous support and containing Pd have an averagethickness of not more than 2 μm.
 20. A hydrogen permeable structureaccording to claim 19, wherein an amount of deposited Pd is not morethan 5 g/m² in the thin films formed on and/or in said porous supportand containing Pd.
 21. A hydrogen permeable structure according to claim18, wherein said porous support is a porous body of silicon nitride. 22.A hydrogen permeable structure according to claim 18, wherein saidporous support is a metallic porous body.
 23. A hydrogen permeablestructure according to claim 18, wherein said porous support has holesin the surface thereof, and said hydrogen permeable structure includes aporous oxide layer, or a layer of metal or metal oxide having an averageparticle size of not more than 2 μm, said layer being formed so as tofill the holes.
 24. A hydrogen permeable structure according to claim23, wherein said oxide layer contains at least one selected from thegroup consisting of aluminum oxide, silicon dioxide and zirconium oxide.25. A hydrogen permeable structure according to claim 23, wherein saidoxide layer is made of aluminum oxide.
 26. A hydrogen permeablestructure including a layer in which pores are sealed off by depositinga metal containing Pd in a porous support and/or porous powder.
 27. Ahydrogen permeable structure according to claim 26, wherein an amount ofnitrogen permeable through said hydrogen permeable structure is not morethan 0.6 ml/min/cm² under a differential pressure of 1 atmosphericpressure.